Refrigeration system



May 25, 1965 J. H. BLAKE REFRIGERATION SYSTEM 2 Sheets-Sheet 1 Filed Oct. 10, 1963 ,.HVHhH lullll vw mm NVENTOR. JUL/AN H. BLAKE BY MM A ATTDRNEYS May 25, 1965 J. H. BLAKE 3,184,926

REFRIGERATION SYSTEM Filed oct. 1o, 196s 2 sheets-sheet 2 PIE--2- LIQUID 508 COLER R565 I VER INVENTOR. JUL/AN H. BLAKE Bvyaw Arron/Veys AIR COOLER CONDENSER United States Patent O 3,184,926 REFRSEMTEN SYSTEM Julian H. Blake, Beimont, Calif., assigner to Ray Winther Company, South San Francisco, Calif., a corporation of California Filed st. iti, 1963, Ser. N 315,174 lil Claims. (Cl. 62-155) rDhis invention relates to improvements in a refrigeration system and more particularly to an improved method `and .apparatus for defrosting refrigerator systems including both low temperat re coils and high temperature coils.

Specifically, this lapplication -is a continuation-impart of my co-pending application Serial No. 178,468, filed March 8, 1962, entitled Method and Apparatus for Defrosting Refrigeration Systems, yand this 'application is now issued as -United States Patent No. 3,150,498.

The great increase in the frozen food industry and the widespread tendency to centralize food stores into large supermarket oper-ations has created -a huge demand for multiple evaporator refrigeration systems. Economy of installation and operation makes it highly desirable to incorporate the evaporator coils of the frozen food counters, and other refrigeration requirements such as walk-in boxes and even .air conditioning in a single centralized refrigeration system.

Frozen foods must be maintained at a temperature of 0 F. or below and these low temperature requirements create considerable problems in connection with the frosting up of the evaporator coils. ln order to prevent un-v ple evaporators of the type set forth. In general, the l t methods used are the same as the methods originally conceived for use with small refrigerators and the like. These meth-ods fall into two basic groups: (l) `def-frosting by the application of external heat such as the `ambient heat of the atmosphere or heat from other external sources, and (2) the heat of compression produced during the refrigeration cycle and which is normally removed from the refrigerant by the condenser. It is the latter basic method of defrosting, commonly known tas the hot gas defrost method, with which the present application is concerned.

Previous hot gas defrost systems have circulated the hot gas to the evaporator either by valving the system to cause the hot gas to cycle through the evaporator in a reverse direction or by isolating the evaporator in such manner as to permit a liquid vapor cycle wherein the liquid returns to the heating point under the influence of gravity. The latte-r system is much too :slow for large scale operation `and requires 'an excessive amount of plumbing.

The reverse cycling hot gas defrost systems present a major disadvantage in that at least a portion of the hot gas is usually condensed into liquid form in the evaporator coil during the defrosting operation. The liquid refrigerant is then drawn into the suction line of the compressor and passes't-herethrough in the form of liquid slugs. If these slugs reach the compressor in liquid form they can cause breakage land other damage. This is commonly called slugging the compressor. Y

To prevent damage to the compressor it has heretofore been necessary to distribute the liquid by revapo-rizing the slugs or by entraining the liquid in the stream of Vaporized refrigerant in the form of small Vatomized lparticles. Either of these methods requires additional expensive apparatus such as heat means for effecting the revapor-ization or injection devices for atomizing the liquid'slugs plus accumulating chambers which act somewhat in the 3,184,926 Patented May 25, 1965 "ice manner of 'surge tanks. Not only is th-e added apparatus expensive but under certain conditions slugging of the compressor is still possible.

It has been proposed to avoid the slugging problems by connecting a pair of evaporators in series with the rst evaporator operating at subfreezing temperatures and the second evaporator operating at above freezing temperatures. With this system only the subfreezing evaporator needs defrosting yand it is possible to cycle the hot gas from the compressor through the subfreezing evaporator, to eifect defrosting thereof, and into the above-freezing evaporator where any liquefied refrigerant will be eX- panded into gaseous form. This i-s really only an adaptation of the revaporizing technique wherein the revaporizing heat is acquired from the air passing over the abovefreezing evaporator coil. While this system is somewhat more efficient than revaporizing by the .addition of external heat or by utilizing the heat of compression, it is rather tricky in operation and will function only where high and low temperature coils are connected in series.

ln both the present applic-ation land my prior application, there is provided a hot gas defrost system wherein the refrigerant liquefied dur-ing the defrosting process is utiized for refrigerating without revaporizing or passing through the compressor, thus adding to the thermal ethciency of the -system and -obviating any requirement for separate vaporizing or yatomizing means.

ln particular, my prior applic-ation shows a system where the low temperature refrigeration coils may be defrosted in accordance with such a principle. However, it is sometimes desirable to provide means for defrosting high temperature refrigeration coils and the present invention relates to -a Isystem whereby high temperature coils which are desired to be defr-osted may be defrosted in accordance with the principles of my 'oo-pending application by adding a minimum amount of equipment to -a normal system. in its pref-erred form, the present invention is combined with that shown in my co-pending application cited above.

According it is a principal object of this invention to provide 4an improved refrigeration system wherein multiple evaporator coils may be selectively defrosted by reverse cycling of the compressed hot gaseous refrigerant `and wherein the cooled and partially liquefied refrigerant will be returned to the liquid refrigerant :supply line for use in refrigerating the other evaporators in the system.

Another object of the present invention is to provide a system of the character described in which both high temperature coils .and low temperature coils may be defrosted.

A further object of the invention is to Iprovide an apparatus of the character described in which the defrosting is accomplished by a pressure differential wherein the pressure in a hot gas defrost line is maintained at a pressure above the pressure in the liquid supply line.

Another object of the invention is to provide a method of defrosting an evaporator coil by supplying hot vapor-V ized refrigerant to the suction line end of the evaporator and controlling the pressure in the liquid refrigerant supply line so as to create a pressure differential across the evaporator unit sufcient to urge refrigerant condensed therein into the liquid refrigerant supply system.

Still another object of the invention is to provide a method and apparatus for accomplishing hot gas defrosting of a plurality of evaporators including both low temperature and high temperature evaporators which are connected in parallel between a liquid refrigerant supply line and their compressor suction lines in which the individual'iow temperature evaporators may be selectively` disconnected from their compressor suction line and connected to a hot gas supply linel having a pressure higher than the pressure in the liquid'refrigerant supply line, and

e hot gas defrost line, for defrosting action.

3 in which reverse ilow'is provided through the high temperature evaporators.

Yet another object of the invention is to provide a large-scale multiple evaporator refrigeration system capable of accomplishing rapid hot gas defrosting of the individual evaporators on demand and with a minimum of controls and plumbing.

Yet still another object of the invention is to provide a refrigeration system of the character described in which slugging of the compressor is completely avoided.

Further objects and advantages of-my invention will be apparent as the specification progresses, and the new and useful features of my refrigeration system will be fully delinedin the claims attached hereto.

In general, the presentinvention provides a method and apparatus for `defrosting all units of a refrigeration system including both high temperature evaporator coils and low temperature evaporator coils by passing hot vaporized refrigerant through the evaporator being defrosted under the inliuence of a pressure differential sufficient to cause cooled and partially liquefied refrigerant to flow into the liquid refrigerant supply line. 'TheV method and apparatus are particularly suited for effecting hot gas defrosting of multiple evaporators connected in parallel, the-apparatus having valves for controlling the pressures in the hot gas supply line and in the liquid refrigerant supply line together with valve means for selectively connecting each ofthe evaporators to either the compressor suction line, for refrigerating action, or to the Y During the defrost action the cooled and partially liquefied refrigerant is injected into the'liquid refrigerant supply line by reason of the described pressure differential, thus making the liquefied refrigerant available for refrigerating action in others of the multiple evaporators and at the same time avoiding problems of slugging the compressor.

As used herein, the term high temperature evaporator means an evaporator which has its suction line connected to thehigh stage suction of a two-stage refrigeration system at a sufciently high pressure so that the evaporation temperature of the refrigerant in the coils is higher than the evaporation temperature of the refrigerant in the low temperature evaporator connected to the low stage suction. Where the coil temperatures are above freezing, frosttdoes not formon the high temperature evaporator coils and, in such a case, means may be provided to prevent any hot gas from entering these coils and unduly heating them. On the other hand, the. term high temperature Ycoils also includes coils in which the evaporation Y temperature of refrigerant is below freezingalthough near Vfreezing and frost does form on such coils. The term low temperature coils is used to mean the coils in which the refrigerant is generally evaporatedfto provideV a coil temperature of from about minus F. to about minus 40 F. and frosting of the coils is particularly acute.

In my prior application, means were provided where- `by the low temperature coils could be eihciently evaporated, but the defrost of the high temperature coils was tion. However, it will be'appreciated that the system for defrosting high temperature coils may also be Vused withl other types of refrigeration systems. i

In a typical system such'as a supermarket,YV as manyY as ten or more groups of high temperature evaporatorsl coolvarious rooms and fixtures such as vegetable dis'- play cases, meat storage coolers, andthe like These evaporators are conventionally-defrosted by timeclocks turning olf their flow of refrigerant until theabov'e freez-V ing air passing over the coils melts them off. ,Alternatively, they may be defrosted by using a three way valve and separate suction line with control of hot gas to effect any of :the prior known hot gas defrosting systems. However, the latter method requires all of the controls necessary to effect defrost of low temperature coils.

ln accordance with the present invention, the defrost of the high temperature loads are accomplished by using hot gas from the discharge of the low stagev booster compressor in a two stage compressor system. This is accomplished by isolating the evaporator systems from the high stage compressor andy receiver so that a new refrigeration cycle is provided in which .the low stage booster drives the refrigerant in reverse through the high ternperature coils and then back to the liquid refrigerant line where it passes into the low temperature coils, is vaporized and returns to the low stage compressor. YThis new cycle is formed by simply shutting off the high stage compressor while simultaneously shutting off the communication betweenthe liquid refrigerant supply line and the receiver and any other associated equipment.

ln a :typical system, the defrost is initiated and terminated by a simple time clock control.y At the start of the cycle, the clock will actuate a relay which stops the highstage compressor and also shuts off the liquid refrigerant supply. In addition, means are preferably provided to retainthe low temperatureevaporators in refrigeration condition and avoid a defrost position of these evaporators in order to provide maximum return of gas to complete the defrosticycle. Defrosting is generally accomplished in about ft'een (l5) minutes, and at the end of this period the control clock switches the system back to normal operation and .the original balance of pressure is generally reached. in two or threeV minutes.

The preferred forms of'my invention are illustrated lin the Vaccompanyingdrawings forming part of this description, in which: i

FIGURE l is a schematic plan view yillustrating a preferred embodiment of the refrigeration system of the present invention, particularly adapted for use Vin supermarkets or the lilrerand FlGURE 2, a schematic plan View, illustrating modified forms of certain of the components of FIGURE l shown in operative association.

While I have shown only thepreferred Vforms of my invention, it should be understood that various changes `or modifications may-be made within thescope ofthe claims attachedy hereto without departing `from-the spirit of the invention. Y

Referring to the drawingsin greater detail and-particularly to FIGURE l, it is seen thattthe defrosting apparatus for refrigeration systems of theV present invention is particularly adaptedV for use in a system havingoneor more lou/.temperature evaporator units ll, 'such asunits 11A; llB and lllC connected betweena liquid'refrigerant supply line ,l2 and a compressor suction line Vl?) together With valve means lid for selectively connecting a hot gas supply line 16 to the evaporator units 1l while at the same time vdisconnectingthe latter from the compressor suction line 13,they system also including kmeans l17 for regulating the pressure inIthe liquid refrigerant supply line l2 so as to create a pressure dierential across the evaporator'unitll suiicientto urge refrigerant condensed therein into the liquid refrigerant supplyline when the refrigeration systems in which rcompressor means f8 compresses a gaseous refrigerant-and propels'it through a conduit v@into` a condensing means'Z adapted to remove a portion V of the lheat energy from the` refrigerant and condense it into liquid form. The liquid refrigerant then passes througha conduit'ZZ into a receiver `'Z3-and from the'receiver into the liquid refrigerant supplyjline 12 for the vevaporator uuitil'.

The evaporator units Irl each 'includey expansion valves 24 adapted for expanding the liquidrefrigerantlin the evaporator coils 26, this action serving to absorb heat energy and reduce the temperature of the coil 26 for refrigeration purposes.

In accordance with the invention of my co-pending application which is used in the preferred form of the present invention, a predetermined pressure differential is maintained between the pressure in the hot gas defrost line, leading from the compressor discharge conduit 19 and the Iliquid refrigerant supply line 12, the pressure differential being suliicient to urge the cooled and at least partially liquefied refrigerant from defrosting evaporator coil 26 into the liquid refrigerant supply line 12 where it will be available for refrigerating the evaporator units not being defrosted. As here shown, the valve means 14 is adapted for selectively connecting the end 27 of the evaporator coil remote from the expansion valve 24 to the compressor suction line 13 during the refrigeration cycle or to the hot gas defrost line 16 during the defrost cycle. When the evaporator unit 11 is in the defrost cycle, the cooled and partially liquefied refrigerant is diverted around the expansion valve 2e by means of a by-pass 28 containing a one-way check valve 29.

As here shown, the means 17 for controlling the pressure in the liquid refrigerant supply line 12 so as to achieve the desired pressure differential between lines 12 and 16 comprises a conventional pressure-regulator valve 31 interposed in the line 12 between the receiver 23 and the first evaporator unit 11. The pressure-regulator valve 31 may be 'of any suitable type and it is preferred to use a conventional pressure-reducing valve of the type well known in the art. l

The valve 31 is adjusted to provide for a pressure in line 12 which is lower than the pressure in the hot gas defrost line 16. The pressure differential should be suticient to cause the refrigerant to move rapidly through the evaporator coil 26 in the direction opposite to its normal direction of flow, the refrigerant passing through by-pass 28 and check valve 29 :and arriving at liquid refrigerant supply line 12 at a pressure higher than the pressure maintained in line 12 by the pressure-regulator valve 31. The cooled refrigerant will thus enter the line 12 and supplement the supply of liquid refrigerant therein for subsequent use in the refrigerating cycles of other evaporator units communicating with line 12, or of the evaporator unit being defrosted, after the defrost cycle is completed. In general, the pressure differential between lines 12 and 16 is maintained by pressure-regulator valve 31. For example, in a typical installation where the discharge pressure of the compressor means is 180 p.s.i., the valve 31 is regulated to provide a pressure of about 165 p.s.i. in the liquid refrigerant supply line 12, thus providing a pressure differential of about 15 p.s.i. The exact pressure differential t-o be used will depend upon the flow characteristics through the evaporator units, but I have found in actual practice that a pressure differential of about p.s.i. to 20 p.s.i. will be sufficient in most installations.

As previously stated, the method and apparatus of Vthe present invention is particularly adapted for use with multiple evaporator installations such as those encoun- Vterred in large food markets wherein a plurali-ty of evaporator units such as units 11A, 11B and 11C are provided for maintaining subzero temperatures in frozen food cabinets and in which additional higher temperature evaporator units 2S are employed for otherpurposes such as -walk-in refrigerators, etc.v A system of this character is depicted schematically in FIGURES l and 2 of the drawings. As there shown, each of the evaporator units 11 andAZS comprise three evaporator coils 26. It should be understood, however, that the number of units and the evaporator vcoils in the particular unit may be varied so long as the described connections are provided.

It is necessary to the purposes of the present invention that the evaporator units 11 be connected in parallel between the liquid refrigerant supply line 12 and the cornpresser suction line 13 so that the refrigerant injected into supply line 12 from the evaporator unit being defrosted may be utilized in the refrigeration cycles of the other evaporator units. I have found it desirable for at least two of the evaporator units to be in their refrigeration cycles for each evaporator unit being defrosted. In order to accomplish such action, the means 14 may be provided in the form of a two-position valve operated by an electrically operated actuating device supplied with electrical energy through appropriate leads. The valves may then be controlled by manual switches or by automatic defrost switching means having provision for ensuring that no more than the desired number of evaporator units are being defrosted at once. In order to synchronize the defrost action with that of the high temperature coils, the controls may be actuated by a common timing device.

As described in my prior application, sub-cooler means 37 is provided for maintaining the liquid refrigerant in the supply line 12 at a temperature sufficiently low to prevent iiash vaporization as the liquid refrigerant passes from the receiver 23 and dryer 38 through the pressureregulator valve 31. The sub-cooling of the liquid refrigerant also tends to cool the refrigerant being injected into line 12 from the evaporator unit undergoing the defrost cycle sufficiently to ensure that any vaporized refrigerant not condensed in the evaporator unit will be condensed to liquid form as it enters the supply line 12.

As here shown, the sub-cooler means includes a subcooler evaporator coil 39 surrounding the liquid refrigerant supply line 12 and having an expansion valve 41 interposed in a conduit 42 connected to the liquid refrigerant supply line 12. An opposite end of coil 39 is connected by means of conduit 43 to the compressor connecting line d5.

As may be seen in the drawings, I prefer to provide a two-stage compressor means 18. This means includes a low-stage booster compressor 4A interposed in the suction line 13 and discharging into a high-stage compressor 46 which discharges into the conduit 19. The conduit 43 is connected to line 45 between the compressors 4d and 46 in the conventional manner for desuperheating the gas entering compressor 46. The sub-cooler evaporator valve 41 may conveniently be operated by a sensing device 47 positioned at the intake side of compressor 46 in the conventional manner.

As best seen in FIGURE l, the high temperature coils are disposed in parallel between the liquid refrigerant supply line 12 and a high temperature suction line 48 which communicates with the connecting line 45 between the low stage compressor 44 and the high stage compressor 46. In other respects, the high stage evaporators 2SA, 25B and 25C are similar to the lOw stage evaporators and are equipped with expansion valves 24 and by-passes 28 containing check valves 29. The purpose of these check valves is to allow reverse flow at defrosting as is accomplished when the low temperature coils are defrosted. However, there is no need fory the two position valves 14 as willi-be explained more fully hereinafter.

In FIGURE l, the refrigeration system is shown with the high temperature coils defrosting, but the drawing will also illustrate the normal cycle simply by considering that the fiow through line 48, the high temperature coils and liquid line 12 has refrigerant flowing in the direction opposite'that shown by the arrows S1. Thus,

^ Y inthe normal refrigeration cycle where movement of refrigerant is shown by dotted arrows Sti in FGURE l,

evaporated refrigerant from the low'stage compressors enters compressor suction line 13 and goes through low stage compressor i4 through vconnecting line 45 to high Stage compressor 46. ln the branch line 45 between compressors, additional refrigerant is picked up from lineia when the liquidV sub-cooler is in refrigerating position and from the high temperature suction line d8 where evaporated refrigerant in the high temperature coils is fed. 'l

alogene ln normal operation, the pressure in line between compressors will be say about 33 pounds per square inch so that the evaporation temperature of refrigerant in the high temperature coils will be higher than that in the low temperature coils. The refrigerant thus entering the high stage compressor 45 is discharged through line vi9 to condenser 2l. where it is liquefied and passes to receiver 23. From the receiver 23, the refrigerant passes through the dryer 3S, liquid sub-cooler 37, and pressure regulator valve 3l` to liquid refrigerant supply line l2. Liquid refrigerant from supply line l2 then passes through the expansion valves 24 as required to supply refrigerant to the evaporators 11 and 25.

In order to defrost the high temperature coils, the

liquid refrigerant supply line is isolated from the receiver by any suitable means such as valve 52 and switch means for simultaneously shutting oli" the high stage compressor. As the high stage compressor is shut off, the ilow through line 43 from the liquid sub-cooler is also shut ofi in any typical system utilizing liquid sub-cooler in this manner in order to protect the compressor. Accordingly, means are also provided for shutting off the flow through the liquid sub-cooler and this provides complete isolation of these components from the system.

For example, as here shown, timer 53 is constructed to provide a signal to the solenoid 54 which in turn opens switch 56 to shut oil the compressor and at the same time provide line voltage into line 57.

and stop the flow of refrigerant through the coils of liquid sub-cooler 37 and into line 43. Simultaneously, solenoid '6l is energized to shut of valve 52. With this operation completed, the low stage compressor 44 and the high temperature coils and low temperaturercoils operate a different refrigeration cycle automatically with the high temperature coils serving as a condenser and simultaneously` becoming defrosted.`

This refrigeration cycle goes into effect because when the high. stage compressor 46 and line l2 are shut ott, the pressure in lines 45 and 48 build up from their normalof about 33 pounds to a pressure of about 8O to 90 pounds. During the defrost of the high temperature coils, the low stage compressor is continuously operated in a conventional manner such as that shown in United States Patent No. 2,895,306. Hot gas will be forced backward through all of the high temperature suction With line S7 energized, solenoid 58 operates to shut off the valve 59` lines building up pressures and temperatures in all high.

temperature evaporators. ln this way, the high temperature evaporators will defrost and simultaneously condense this discharge gas. The condensed liquid will then leave the evaporators via their check valves 29` and will enter the liquid supply line l2 where it will be reused by the Vlow temperature evaporators. The refrigeration in the low temperature` evaporators operates normally supin,- abouttfteen i 54 and replacing switch 56. With the high stage comi" pressorbaclr in operation, the pressurein line 45 ispsoonv back toits normal of 33 and all systems operate infthe normal way. This return is generally raccomplished in` Y i'trccordingly,` itV is .seenlv that the high temperature coilsmay be defrostedin'a Ysystem of thisY nature by a simpleoperation requiring a about two to three; minutes.-

" trolled coil .temperature ',whichgis regulated by pressure` v regulator 64; regulator is usedtojcontrol the pres-,r v sure inthe coill atthe pressure corresponding tothe d.eY

minimum of valvin'gcontrols and only a common high",

temperature `suction line, the operation also maintaining a high level of refrigeration eiliciency.

- In order to Vdefrost oneof Vthe low Atemperature coils,

, thevalve means 14 for the particular evaporator will be,

' Vdisplaced to `its-*other position communicating the evapora-l t tor coils with the hot gassupply line 16 rFor example,

- 8 assume valve la ofA evaporator 11B is changed tothe defrost position, t

With the pressurerin line lo at say psi., the hot gas will. flow in a reverse direction .through the evaporator coils 26, the bypass 2d and the check valve 29 of unit llB and into the liquid refrigerant supply line l2.

Should a more rapid defrosting action be desired, the:

pressure-regulating valve 3l should be adjusted to provide a greater pressure differential between lines l2 and lo. Conversely, if itis desired to slow down the defrosting action, the valve 31 could be adjusted to provide a lesser pressure differential. For most purposes, a differential of approximately l5 p.s.i. will be preferred,

vAs the hot vaporized refrigerant passingthrough coils 25 gives up its heat energy to eiect defrosting, it becomes wholly or partially condensed and the cooled refrigerant asses through. lay-pass 28 and checkuvalvef29 into the liquid refrigerant supply line l2.y This cooled refrigerant adds to and supplements the liquid refrigerant Yllowing through the line l2 andfis used during the refrigeration cycles of the other evaporator units llA, 11C and the high temperature units 25.

K It is highly desirable that at least two evaporater units be in refrigeration condition tor each evaporator .unit which is in defrost condition in order to provide. a supply of gas tothe compressor which is adequatek for rapid defrosting. lf desired, one or more .of the evaporatorV units in the refrigeration cycle can "be blocked open while another unit is being detrosted so as to permit constant operation of the compressor and consequent continuous defrosting action. Y

A more complete description of the defrosting operation of the low temperature coils is given in my co-pending application cited above.

In FIGURE 2, there is shown a refrigeration system somewhat similar to that shown in FlGUREl except that it illustrates certain alternativeforms of theyinvention.

Although all of these alternatives are illustrated in FlG- URE 2, it will be appreciated that they may he used severally in any `,desired combination or in total as shown.r Y As thereshown, the system is similar to that shown in FGURE l except for modifications in the evaporators. Thus, there are two low temperature evaporator units 11D andllE` and -three high temperature evaporators 25A, 25D and 25E.Y

The evaporator units MD and 51E are similar to units lliA, lllB and 11C-except thatmeans 62 are provided to by-pass the thermostats and `maintain liquid supply to expansion valves 2d at all times the high temperature coils are defrostingf. This Yis accomplished by a signal .in line 63 that overrides the thermostats. t Y Y n The purpose of keeping these units open to thesupply line `1s to positively assure movement ot' refrigerant through the high temperature coils and thereby complete the defrost operation during the programmed time of say fifteen-(l5) minutes. NoV harm is done-by operating the low temperature coils in thisway without demand from the thermostats, because the duration is short andtheresulting 'Y overcooling is allowable; VSuch a system is inilportaintY is' large in comparison where the high vtemperature Yload to the-lowtemperature load. f t

The high temperature evaporator units include the-unit 25A similarto'that ofl FIGURE 1,1unit 25Dwhich operates atta higher,,coilrteniperature vthan-unit 25A and unity 25E whichrequires nodefrosting attall. lrUnit ZSDhas a consired'boilingttemperature of refrigerant. Y l

The coil temperature'of unit 25D is stilllbelow reeaing,

andthe unitis designed-to defrost ini-theysarne manner as, unit 25A. However, itis `fo'undfthatf when gas is forcedin reverse `-through afftypical pressure regulator valve, a pressure drop ,of 7 to. l0:p,s;i.v usuallyresultsp- In Vorder to, avoid .this resistancetothe how ofhotgas during I snaaoae defrost, a by-pass 66 is provided. A check valve 67 is provided to prevent ow through the by-pass during the refrigeration operation of unit 25D.

Unit 25E has a pressure regulator 68 to control its coil temperatures at 32 F. or above. Accordingly, no frost forms and no defrosting is necessary. ln order to avoid wasted passage of hot gas through this unit and the corresponding ineicient operation that would otherwise result, a check valve 69 is provided to prevent defrost gas from entering the unit. With no reverse ow required, by-pass 28 and check valves 29 are omitted from this embodiment. Since the high temperature defrost operation takes place in about fifteen (l) minutes, the temperature conditions of the unit ordinarily do not change substantially and isolation thereof is harmless.

From the foregoing it will be seen that I have provided a novel method and apparatus for defrosting a refrigeration system in which the thermal eflic-iency of the system is increased while completely eliminating any necessity of separate apparatus for revaporizing or atomizing the cooled defrost refrigerant, since such refrigerant is not returned to the compressor directly, but rather is added to the liquid refrigerant supply. In addition I have provided a novel means for controlling the pressure differenrial between the hot gas supply and the liquid refrigerant supply line so as to afford the described mode of operation of the invention.

I claim:

l. A refrigeration system, comprising a liquid refrigerant supply line, a compressor suction line, a plurality of low temperature evaporators connected in parallel between said liquid -refrigerant supply and the compressor suction line, a low stage compressor in position to receive gas from the compressor suction line, a high stage compressor, a connecting line between the low stage compressor and the high stage compressor, a high temperature suction line connected to said connecting line, a high temperature coil between said high temperature suction line and said liquid refrigerant supply line, means for simultaneously shutting off the high stage compressor and the supply to the liquid refrigerant supply line during a timed period when the low temperature evaporators are maintained in refrigeration condition whereby the low stage compressor will supply hot gaseous refrigerant in reverse flow through the high temperature coils to defrost the coils and liquefy the gas which then enters the liquid refrigerant supply line to supply liquid refrigerant to the low temperature evaporators and back to the low stage compressor to complete the cycle.

2. A refrigeration system, comprising a liquid refrigerant supply line, a compressor suction line, a plurality of low temperature evaporators connected in parallel between said liquid refrigerant supply and the compressor suction line, a low stage compressor in position to receive gas from the compressor suction line, a high stage compressor, a connecting line between the low stage compressor and the high stage compressor, a high temperature suction line connected to said connecting line, a plurality of high temperature coils between the liquid refrigerant supply line and the high temperature suction line, at least one of said high temperature coils having a check valve between the coil and the high stage compressor suction line to prevent defrosting thereof while at least some of the high temperature coils have open lines to allow refrigerant to pass therethrough in reverse direction, and means for simultaneously shutting off the high stage compressor and the supply to the liquid refrigerant supply line during a timed period when the low temperature f evaporators are maintained in refrigeration condition whereby'the low stage compressor will supply hot gaseous refrigerant in reverse flow through the high temperature coils to defrost the coils and liquefy the gas which then enters the liquid refrigerant supply line to supply liquid refrigerant to the low ltemperature evaporators and back to the low stage compressor to complete the cycle.

3. The refrigeration system defined in claim 2 in which certain of the high temperature coils contain a pressure regulator valve between the coil and the high stage compressor suction line whereby the evaporation pressure of liquid refrigerant in the coils is regulated, and a bypass is provided around said pressure regulator valve to allow hot gas to ilow freely in reverse direction during the defrost cycle.

4. A refrigeration system, comprising a liquid refrigerant supply line, a compressor suction line, a plurality of low temperature evaporators connected in parallel between said liquid refrigerant supply and the compressor suction li-ne, a low stage compressor in position to receive gas from the compressor suction line, a high stage compressor, a connecting line between the low stage compressor and the high stage compressor, a high temperature suction line connected to said connecting line, a high temperature coil between said high temperature suction line and said liquid refrigerant supply line, a condenser, a line between the high stage compressor and the condenser, a receiver, a line between the receiver and the condenser, said receiver being in communication with said liquid refrigerant supply line, a hot gas defrost line in communication with the lines between the high stage compressor and the condenser, valve means on each of the low temperature evaporators for changing the cornrnunication of the evaporator coils from the compressor suction line to the hot gas defrost line, and means for shutting off the high stage compressor and the liquid refrigerant supply line and provide a defrost refrigeration cycle in which hot gas from the low stage compressor is forced in reverse fashion through the high temperature suction line to the high temperature coils being defrosted in which it is condensed and thence to the liquid refrigerant supply line.

5. A refrigeration system, comprising a liquid refrigerant supply line, a compressor suction line, a plurality of low temperature evaporators connected in parallel between said liquid refrigerant supply and the compressor suction line, a low stage compressor in position to receive gas from the compressor suction line, a high stage compressor, a connecting line between the low stage compressor and the high stage compressor, a high temperature suction line connected to said connecting line, a high temperature coil between said high temperature suction line and said liquid refrigerant supply line, a condenser, a line between the high stage compressor and the condenser, a receiver, a line between the receiver and the condenser, said receiver bei-ng in communication with said liquid refrigerant supply line, a hot gas defrost line in communication with the lines between the high stage compressor and the condenser, valve means on each of the low ternperature evaporators for changing the communication of the evaporator coils from the compressor suction line to the hot gas defrost line, and means for simultaneously shutting off the high stage compressor and the supply to the liquid' refrigerant supply line during a timed period when the low temperature evaporators are maintained in refrigeration condition whereby the low stage compressor will supply hot gaseous refrigerant in reverse flow through the high temperature coils to defrost the coils and liquefy the gas which then enters the liquid refrigerant supply line to supply liquid refrigerant to the low temperatureevaporators and back to the low stage compressor to complete the cycle.

6. A refrigeration system, comprising a liquid refrigerant supply line, a` compressor vsuction line, a plurality of low temperature evaporators connected in parallel between said liquid refrigerant supply and the compressor suction line, a low stage compressor in position to receive gas from the compressor suction line, a high stage compressor, a connecting line between the low stage'compressor and the high stage compressor, a high temperature suction line connected to said connecting line, a plurality supply line and the high temperature suction line, at least one of said high temperature coils having a check valve between the coil and the high stage compressor suction line to prevent defrosting thereof While at least some of the high temperature coils have open lines to allow refrigerant to pass therethrough in reverse direction, a condenser, a line between the high stage compressor and the condenser, a receiver, a line between the receiver and the condenser, said receiver being in communication with said liquid refrigerant supply line, a hot `gas defrostline in communication with the lines between the high stage compressor and the condenser, valve means on each of the low temperature evaporators for changing `the cornrnunication of the evaporator coils from the compressor suction line to the hot gas defrost line, and means for simultaneously shutting oif the high stage compressor and the supply to the liquid refrigerant supply line during a timed period when the low temperature evaporators are maintained in refrigeration condition whereby the low stage compressor will supply hot gaseous refrigerantin reverse how through the high temperature coils to defrost the coils and liquefy the gas which then enters the liquid refrigerant supply line to supply liquid refrigerant to the low temperature evaporators and back tothe low f' stage compressor to complete the cycle. v

7. The refrigeration system defi-ned in claim 6, in which certain of the high temperature coils contain a pressure regulator valve between the coil and the high stage compressor suction line whereby the evaporation pressure of liquid refrigerant in the coils is regulated, and a bypass is provided around said pressure regulator valve to allow hot gas to flow freely in reverse direction during the de'- frost cycle.

8. In a refrigeration system containing a liquid refrigerant supply line, a compressor suction line, a plurality of low temperature evaporators connected in parallel f high temperature evaporator coils connected in parallelbetween the high temperature suction line andthe refrigerant supply line, a valve in the liquid refrigerant supply line, and means for simultaneously shutting ol the high stagecompressor and the valve inthe liquid refrigerantsupply line wherebyrefrigerantdischarge gas from the low stage compressor is forced in reverse fashion through theV high temperature-suction line to the high ytemperature coils in which it condenses while defrosting the high temperature coils and the condensed refrigerant moves to the liquidrefrigerant supply line and thence back to the low stage compressor.

9. The refrigeration system defined in claim 8, in which the means for simultaneously shutting olf the high stage compressor and the .valve in theliquid refrigerant supply line includes an electrical control system operated from a timer, Y

10. The refrigeration system defined in claim 9, in which the control system includes mea-ns for retaining low of refrigerant to the low temperaturecoils whereby all low temperature coils are operative to ,receive refrigerant during the defrost of the high temperature coils.

1l. The refrigeration system defined in claim 8, in which certain of the high temperature coilscontain a pressure regulatorrvalve between the' coil and the high lstage compressor suction line whereby the evaporation pressure of liquid refrigerant in the coils isy regulated, and a bypass is provided around said pressure regulator valve to allow hot gas to iiow freely in reverse direction during the defrostcycldat ieast one of said high ternperature coilshaving a check valve between the coil and the high stage compressor suction kline kto prevent defrosting thereof while at least some of the high temperature coils have open lines to Vallow refrigerant to pass therethrough in reverse direction.

Retoreuces Cited by the Examiner YUNITED STATES PATENTS 2,389,452 V11/45 yPatterson 62--510'X 2,458,589 1/49 Groat 62-278 2,582,908 2/52 Backstrom f 62-199 X k2,632,305 3/53 MattesonV 62-217 X 2,841,962 v 7/58y Richards 62-175 X Rohner A. OLEARY, Primary Examiner. 

1. A REFRIGERATION SYSTEM, COMPRISING A LIQUID REFRIGERANT SUPPLY LINE, A COMPRESSOR SUCTION LINE, A PLURALITY OF LOW TEMPERATURE EVAPORATORS CONNECTED IN PARALLEL BETWEEN SAID LIQUID REFRIGERANT SUPPLY AND THE COMPRESSOR SUCTION LINE, A LOW STAGE COMPRESSOR IN POSITION TO RECEIVE GAS FROM THE COMPRESSOR SUCTION LINE, A HIGH STAGE COMPRESSOR, A CONNECTING LINE BETWEEN THE LOW STAGE COMPRESSOR AND THE HIGH STAGE COMPRESSOR, A HIGH TEMPERATURE SUCTION LINE CONNECTED TO SAID CONNECTING LINE, A HIGH TEMPERATURE COIL BETWEEN SAID HIGH TEMPERATURE SUCTION LINE AND SAID LIQUID REFRIGERANT SUPPLY LINE, MEANS FOR SIMULTANEOUSLY SHUTTING OFF THE HIGH STAGE COMPRESSOR AND THE SUPPLY TO THE LIQUID REFRIGERANT SUPPLY LINE DURING A TIMED PERIOD WHEN THE LOW TEMPERATURE EVAPORATORS ARE MAINTAINED IN REFRIGERATION CONDITION WHEREBY THE LOW STAGE COMPRESSOR WILL SUPPLY HOT GASEOUS REFRIGERANT IN REVERSE FLOW THROUGH THE HIGH TEMPERATURE COILS TO DEFROST THE COILS AND LIQUEFY THE GAS WHICH THEN ENTERS THE LIQUID REFRIGERANT SUPPLY LINE TO SUPPLY LIQUID REFRIGERANT TO THE LOW TEMPERATURE EVAPORATORS AND BACK TO THE LOW STAGE COMPRESSOR TO COMPLETE THE CYCLE. 